Liquid crystal display device and its drive method

ABSTRACT

A MVA type liquid crystal panel is slow in a response speed when a black state at a drive voltage about 1V is switched to a low brightness halftone state at the drive voltage about 2 to 3V. According to the present invention, in a liquid crystal display device for driving the MVA type liquid crystal panel, when a liquid crystal pixel at a pixel electrode is changed from a first transmittance to a second transmittance greater than the first transmittance, a drive voltage greater than a first target drive voltage in correspondence with a second transmittance is applied to the pixel electrode in a first frame period of changing to the second transmittance, and the first target display voltage is applied from a second frame period. According to the present invention, even when either switching is performed from a black state to a low brightness halftone state, from the black state to a high brightness halftone state, or from the black state to a white state, a response time is shortened, and the switching can be performed without generating an overshoot.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation of International Applicationnumber PCT/JP99/06189, filed Nov. 5, 1999, the entire contents of whichare herein incorporated by the reference.

TECHNICAL FIELD

The present invention relates to a liquid crystal display device and itsdrive method, and in particular to the liquid crystal display device inwhich a liquid crystal having minus dielectric constant anisotropy isaligned vertically when non-voltage is applied; and its drive method.

BACKGROUND ART

At present, in a liquid crystal panel which carries out active matrixdrive by use of a thin film transistor (hereinafter called TFT), itsmainstream is a TN (Twisted Nematic) mode liquid crystal panel in whicha p type liquid crystal having positive dielectric anisotropy is alignedhorizontally to a substrate when non-voltage is applied, and is drivenvertically to the substrate when voltage is applied.

With the progress of late manufacturing technology, the TN mode liquidcrystal panel has been improved conspicuously in contrast, a gradationcharacteristic, and color reproducibility seen from the facade of theliquid crystal panel. However, the TN mode liquid crystal mode hasdrawbacks that a viewing angle is narrower than CRT, etc., and for thisreason there is a problem that the use is restricted.

For the purpose of improving the drawback of the TN mode liquid crystalpanel that the viewing angle is narrow, we, the applicant of thisinvention, developed a MVA (Multidomain Vertical Alignment) type liquidcrystal panel which drives horizontally, when voltage is applied, liquidcrystal molecules aligned vertically when non-voltage is applied, and inwhich an alignment direction of the liquid crystal molecules in onepixel is divided into a plurality of parts, and disclosed the structurein Japanese Patent Application Laid-Open No. 10-185836, etc.

The MVA type liquid crystal panel uses an n type liquid crystal havingnegative dielectric anisotropy and the MVA type liquid crystal panel isprovided with domain restriction means for, when voltage is applied,restricting an alignment direction of the liquid crystal so that thedirection is set to be a plurality of parts in one pixel.

The domain restriction means incline in advance the liquid crystalmolecules at a projection part at a slight angle when non-voltage isapplied, by the projection, etc. provided in a part on an electrode.This projection performs a role of a trigger for determining thealignment direction of the liquid crystal molecules when voltage isapplied, and any small projection is enough. Incidentally, as the MVAtype liquid crystal panel inclines in advance the liquid crystalmolecules at a slight angle by the domain restriction means, a rubbingprocess to a vertical alignment layer or alignment film is unnecessary.

In the MVA type liquid crystal, in a state that non-voltage is applied,most of liquid crystal molecules are aligned vertically to a surface ofthe substrate, and the transmittance becomes a status of 0 (blackstate). When an intermediate voltage is applied, the inclinationdirection of the liquid crystal molecules is determined under theinfluence of an inclined plane of the projection, and the alignmentdirection of the liquid crystal in one pixel is partitioned.Accordingly, the intermediate voltage causes an optical characteristicof the liquid crystal in one pixel to average, thereby obtaining ahalftone state uniform in all directions. Furthermore, when apredetermined voltage is applied, the liquid crystal molecules aresubstantially horizontal to change to a white state.

However, in the MVA liquid crystal panel, there is a problem that aresponse speed when a black state at a drive voltage of about 1V isswitched to a low brightness halftone state at a drive voltage of about2 to 3V is slower than the TN mode liquid crystal panel.

It is considered that this is because, since the rubbing process in thevertical alignment film is not carried out in the MVA type liquidcrystal and the alignment directions of the liquid crystals in a fineregion direct to various directions in a state that non-voltage isapplied, when a drive voltage is low at about 2 to 3V, it takes sometime to align the alignment directions of all the liquid crystals topredetermined directions.

Furthermore, when the black state at the drive voltage of about 1V isswitched to a high brightness halftone state at the drive voltage ofabout 3 to 4V, or when the black state at the drive voltage of about 1Vis switched to a white state at the drive voltage of about 5V, as thebrightness is overshot, there is a problem that a display impression isworse.

It is considered that this is because, as a moment of rotating thealignment direction of the liquid crystal increases at the drive voltageof about 3V or more, the alignment direction of the liquid crystalrotates over the target alignment direction.

Furthermore, when the black state is switched to a halftone state or so,the halftone state or so is affected by not only the black state shortlybefore that but also a further previous display state, and thebrightness may be overshot. It is considered that this is because thealignment state of the liquid crystal in the black state shortly beforethat differs due to the previous alignment state of the liquid crystal.

Then, it is an object of the present invention to provide a liquidcrystal display device having a drive circuit in which when driving theMVA type liquid crystal panel in which n type liquid crystals arealigned vertically, a response time when the black state is switched tothe low brightness halftone state is lessened, and the overshoot whenthe black state is switched to the halftone state or the white state isdiminished; and its drive method.

DISCLOSURE OF THE INVENTION

The above object is attained by providing the following liquid crystaldisplay device: The liquid crystal display device includes domainrestriction structure for restricting so that a liquid crystal isprovided between a pixel electrode and a counter electrode to whichvoltage is applied, and an alignment of the liquid crystal issubstantially vertical when non-voltage is applied, substantiallyhorizontal when a predetermined voltage is applied, and inclined when asmaller voltage than the predetermined voltage is applied, and further adirection that the alignment of the liquid crystal is inclined is set tobe a plurality of parts in each pixel when a voltage smaller than thepredetermined voltage is applied, and further comprises.

A drive circuit in which when the pixel is changed from a firsttransmittance to a second transmittance greater than the firsttransmittance, a voltage greater than a first target drive voltagecorresponding to the second transmittance is applied on a pixelelectrode in a first period of changing to the second transmittance, andthe first target display voltage is applied in a second period after thefirst period.

According to the present invention, when the liquid crystal in the pixelis changed from the first transmittance to the second transmittance, asa voltage greater than the first target drive voltage is applied in thefirst period, and the first target display voltage is applied in thesecond period after the first period, in the MVA type liquid crystalpanel in which the alignment directions of the liquid crystal in aminute region direct to various directions in a state that a voltage isapplied, the response time when the alignment direction of the liquidcrystal therein is changed can be reduced. Accordingly, it is possibleto provide the liquid crystal display device with a wide viewing angleand a superior response characteristic.

Furthermore, in the drive circuit of the liquid crystal display deviceaccording to the present invention, when the pixel is changed from thefirst transmittance to a third transmittance greater than the secondtransmittance, a second target drive voltage in correspondence with thethird transmittance is applied on the pixel electrode in the firstperiod of changing to the third transmittance.

According to the present invention, when the liquid crystal in the pixelis changed from the first transmittance to the third transmittance muchgreater than that, as the second target drive voltage in correspondencewith the third transmittance is applied in the first period, it ispossible to reduce the response time without causing the overshoot withrespect to the change in the alignment of the liquid crystal.Accordingly, it is possible to provide the liquid crystal display devicewhich is free of flicker due-to the overshoot, and has the superiorresponse characteristic.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an equivalent circuit of a MVA type liquid crystal panelaccording to an embodiment of the present invention;

FIGS. 2A and 2B are schematic views of the MVA type liquid crystal panelaccording to the embodiment of the present invention;

FIGS. 3A, 3B and 3C are waveform diagrams of a drive voltage of a liquidcrystal display device according to the embodiment of the presentinvention;

FIGS. 4A and 4B are response characteristic diagrams (I) oftransmittance of the MVA type liquid crystal panel according to theembodiment of the present invention;

FIGS. 5A and 5B are response characteristic diagrams (II) oftransmittance of the MVA type liquid crystal display panel according tothe embodiment of the present invention;

FIGS. 6A and 6B are diagrams for explaining the response characteristicof transmittance;

FIG. 7 is a response characteristic diagram (III) of transmittance ofthe MVA type liquid crystal panel according to the embodiment of thepresent invention;

FIG. 8 is a relational diagram between a drive voltage and acompensation voltage according to the embodiment of the presentinvention;

FIG. 9 is a schematic view of the entire of the liquid crystal displaydevice according to the embodiment of the present invention;

FIG. 10 is a cross-sectional view when a drive voltage is not applied onthe MVA type liquid crystal panel according to the embodiment of thepresent invention;

FIG. 11 is an explanatory view when the drive voltage is applied on theMVA type liquid crystal panel according to the embodiment of the presentinvention;

FIG. 12 is a diagram showing a relationship between the drive voltageand the panel transmittance;

FIG. 13 is a diagram showing a relationship between the drive voltageVoff and a response time to a halftone;

FIG. 14 is a cross-sectional view of the MVA type liquid crystal panelaccording to the embodiment of the present invention;

FIG. 15 is a top view of the MVA type liquid crystal panel of FIG. 14;

FIG. 16 is a diagram showing a relationship between the drive voltageand the panel transmittance after lamination of a retardation film;

FIG. 17 is a cross-sectional view of the MVA type liquid crystal panelaccording to the embodiment of the present invention;

FIG. 18 is a top view of the MVA type liquid crystal panel of FIG. 17;

FIG. 19 is a structural view of the liquid crystal display deviceaccording to the embodiment of the present invention;

FIGS. 20A, 20B and 20C are explanatory views showing a compensationprinciple according to the embodiment of the present invention;

FIG. 21 is a waveform diagram when an overshoot generates in a firstframe under influences of a −2 frame;

FIG. 22 is a diagram showing a relationship between a drive voltage Vn−2of the −2 frame and maximum transmittance Tp1 of the first frame;

FIG. 23 is a diagram showing a relationship between a drive voltage Vn−3of a −3 frame and the maximum transmittance Tp1 of the first frame;

FIG. 24 is a waveform diagram when the overshoot generates whentemperatures rise;

FIG. 25 is a diagram showing a relationship between the maximumtransmittance Tp1 of the first frame and a drive voltage Vn−1 shortlybefore that; and

FIG. 26 is a diagram showing a relationship between the maximumtransmittance Tp1 of the first frame and the drive voltage Vn−1 shortlybefore that at 45° C.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the present invention will be describedwith reference to the drawings. However, such the embodiment does notrestrict a technical scope of the present invention.

[First Embodiment]

FIG. 1 is an equivalent circuit of a MVA type liquid crystal panel 1according to an embodiment of the present invention. The actual MVA typeliquid crystal panel 1 has 1024×3×768 pixels, for example, when a colordisplay is made, but here shows the case of 3×3 pixels.

The MVA type liquid crystal panel 1 is assorted into respective pixelsby longitudinal source electrode lines S0, S1, S2 and transverse gateelectrode lines G0, G1, G2, and has TFTs 2 to 10 in each of respectivepixels. A source electrode S and a gate electrode G of the TFTs 2 to 10are connected to the source electrode lines S0 to S2 and the gateelectrode lines G0 to G2, respectively, and a drain electrode D isconnected to pixel electrodes 12 to 20.

The pixel electrodes 12 to 20 are transparent electrodes of ITO (IndiumTin Oxide), etc., and a drive voltage is applied on liquid crystalpixels 22 to 30 inserted between the pixel electrode and a countercommon electrode 32. The common electrode 32 is an ITO transparentelectrode covering the substantially entire plane of a liquid crystalpanel, and a common voltage Vcom is applied thereon.

FIG. 2 is a schematic view of the MVA type liquid crystal panel 1according to this embodiment, and FIG. 2A is a plane view seen fromupward of partial pixel electrodes 15 to 17 in FIG. 1, and FIG. 2B is across-sectional view taken along line A—A of FIG. 2A.

As shown in FIG. 2A, a projection 40 bending zigzag is provided on thepixel electrodes 15 to 17 . This projection 40 functions as domainrestriction structure which splits its alignment direction of a liquidcrystal in one pixel into a plurality of parts. The pixel electrode 16exists in a part assorted by a source electrode line S1 and a gateelectrode line G1, and is connected to a TFT 6. Incidentally, a CSelectrode 41 is an electrode for forming auxiliary capacitance.

Furthermore, as shown in FIG. 2B, the projections 40 are formedalternately in both the common electrode 32 and pixel electrodes 15 to17, and a vertical alignment film (not shown) is provided thereon.Liquid crystal molecules 42 are aligned substantially vertically to asurface of an electrode by a vertical alignment film when non-voltage isapplied, but as the vertical alignment film is not rubbed, the liquidcrystal molecules 42 existing on a lateral inclined plane of theprojection 40 are apt to align vertically to the inclined plane.Therefore, the liquid crystal molecules 42 of the part are inclined atonly a predetermined angle.

The liquid crystal molecules 42 inclined in a part of the projection 40perform such a trigger role as determining alignment directions of theother liquid crystal molecules 42 when voltage is applied. For thisreason, when voltage is applied, as the directions that the liquidcrystal molecules 42 are inclined are split into a plurality of parts inone pixel, visual angle dependency disappears, thereby obtainingomnidirectional uniform display.

FIG. 3 is a waveform diagram of a drive voltage of the liquid crystaldisplay device according to the embodiment of the present invention.FIG. 3A is a waveform of a gate voltage Vg to be applied on a gateelectrode of TFT, and FIGS. 3B and 3C are examples of waveforms of asource voltage Vs to be applied on a source electrode of the TFT. Whenthe TFT is energized by applying the gate voltage Vg, this sourcevoltage Vs becomes a drive voltage to be applied on respective liquidcrystal pixels 22 to 30.

For example, in FIG. 1, if the source voltage Vs is applied on thesource electrode line S1, and the gate voltage Vg is applied on the gateelectrode line G1, TFT 6 is conductive and the drive voltage is appliedon the pixel electrode 16 corresponding to the liquid crystal pixel 26.

Furthermore, the source voltage Vs of FIGS. 3B and 3C, is inverted everyframe period with reference to a potential Vcom of the common electrode32. This is because, since if a unidirectional voltage is always appliedon the liquid crystal, the liquid crystal is deteriorated, the liquidcrystal is driven at AC voltage.

FIG. 3B shows the case where a non-inverted drive voltage Vp is appliedon the liquid crystal pixel in a first frame period Tf1 starting fromtime 0 and in a third frame period Tf3 starting from time 2T, and theinverted drive voltage Vp is applied thereon in a second frame periodTf2 starting from time T and in a fourth frame period Tf4 starting fromtime 3T. Generically, an alignment change of the liquid crystal due tothe drive voltage application is slow, and for changing the liquidcrystal alignment to transmittance in correspondence with the drivevoltage Vp, it is necessary that the drive voltage Vp is continuouslyapplied over several frame periods. In the drive voltage waveforms ofFIG. 3B, Vp is continuously applied over first to fourth frame periodsin the same manner as such conventional drive voltage waveforms.

FIG. 3C shows an improved drive voltage waveform according to theembodiment of the present invention, and for improving a response speedand an overshoot of the liquid crystal pixel, a drive voltage Vp1 of thefirst frame period Tf1 is greater than a drive voltage Vp2 of a secondframe period Tf2 and on.

According to the embodiment of the present invention, in correspondencewith a type of transmittance change of the liquid crystal in the pixel,the drive voltage waveform of FIG. 3C and the drive voltage waveform ofFIG. 3B are distinguished occasionally. Namely, a drive voltage ratioVp1/Vp2 which optimizes the response speed and overshoot is differentaccording to a target transmittance of the liquid crystal pixel. Then, aresponse characteristic of the transmittance will be explained below.

FIGS. 4 to 7 are diagrams for explaining the response characteristic oftransmittance of the MVA type liquid crystal panel 1 according to theembodiment of the present invention. FIG. 4A shows the responsecharacteristic, in a case where the target drive voltage Vp2 is set as2.5V in order to change transmittance of a certain liquid crystal pixelfrom 0% to about 2%, when the drive voltage Vp1 of the first frameperiod Tf1 is set to be 0.8 times the drive voltage Vp2 of the secondframe period Tf2 and on (Vp1/Vp2=0.8), and when the drive voltage Vp1 isequal to the drive voltage Vp2 (Vp1/Vp2=1), and when the drive voltageVp1 is set to be 1.25 times the drive voltage Vp2 (Vp1/Vp2=1.25).

Furthermore, FIG. 4B shows the response characteristic in a case wherethe target drive voltage Vp2 is set as 3V in order to changetransmittance from 0% to about 8%, when the drive voltage Vp1 is equalto the drive voltage Vp2 (Vp1/Vp2=1), and when the drive voltage Vp1 isset to be 1.1 times the drive voltage Vp2 (Vp1/Vp2=1.1), and when thedrive voltage Vp1 is set to be 1.25 times the drive voltage Vp2(Vp1/Vp2=1.25), and when the drive voltage Vp1 is set to be 1.4 timesthe drive voltage Vp2 (Vp1/Vp2=1.4), and when the drive voltage Vp1 isset to be 2 times the drive voltage Vp2 (Vp1/Vp2=2).

From the response characteristic of FIG. 4, when a black state havingtransmittance of almost 0% is switched to a low brightness halftonestate having transmittance of about 10%, if the drive voltage ratioVp1/Vp2 is set as 1.25, it is understood that the response time islessened without the overshoot. Namely, the alignment change of theliquid crystal is completed in about a 1-frame period (T=16.7 ms) fromswitching of the display, thereby changing to the target transmittance.

On the other hand, when Vp1/Vp2 is set to be 0.8, 1 and 1.1, theresponse speed is slow and it takes a 2-frame period or more until theliquid crystal reaches the target transmittance. If so, when ananimation, etc. is displayed, an image is hard to see as the image fallsinto disorder. Furthermore, when Vp1/Vp2 is set to be 1.4 and 2, theresponse speed is fast, but an overshoot of the transmittance isgenerated and this contributes to a flicker of a display screen.

As described above, the vertical alignment film of the MVA type liquidcrystal panel 1 is not rubbed, therefore the alignment directions of theliquid crystal in a minute region direct to various directions in astate that non-voltage is applied. For this reason, when thetransmittance is changed from 0 to a second transmittance, it isconsidered that as the target drive voltage Vp2 in correspondence withthe second transmittance is a low voltage of about 2 to 3V, it takes alot of time to rotate the alignment directions of all the liquidcrystals to a predetermined direction. Accordingly, it is consideredthat if the drive voltage Vp1 of the first frame period is set to be1.25 times the target drive voltage Vp2, an optimal rotation moment canbe given to liquid crystal molecules, and the response speed of theliquid crystal can be reduced.

In this method, when a black state having transmittance of almost 0% isswitched to a low brightness halftone state having transmittance ofabout 10% or less, a drive waveform of FIG. 3C is preferable. With thisdrive waveform, as shown in FIG. 4, the target transmittance can bereached in a 1-frame period. Accordingly, the response completion ispossible in each frame and an animation display is smoothed.

FIG. 5A shows the case where the target drive voltage Vp2 is set to be3.5V so that transmittance is changed from 0% to about 12%, and thedrive voltage Vp1 of the first frame period is set to be 0.8, 1 and 1.25times the target drive voltage Vp2.

In this method, when the black state is switched to a high brightnesshalftone state that transmittance is about 10 to 15%, if the drivevoltage ratio Vp1/Vp2=1, it is comprehensive that the response time isdecreased without the overshoot. In this case, when Vp1/Vp2=0.8, theresponse speed is slow, inversely when Vp1/Vp22=1.25, the response speedis fast, but the overshoot is generated to contribute to a flicker of adisplay screen.

It is considered that this is because when the target drive voltage Vp2is about 3V or more, as a moment of rotating the alignment direction ofthe liquid crystal increases, if Vp1/Vp2 is increased, this contributesto the overshoot, inversely as the target drive voltage Vp2 is high, theresponse speed is sufficiently short even at the drive voltage ratioVp1/Vp2=1.

FIG. 5B shows the case where the target drive voltage Vp2 is set to be5.5V in order to change transmittance from 0% to about 16%, and thedrive voltage Vp1 of the first frame period is set to be 0.8, 1 and 1.25times the target drive voltage Vp2.

In this method, when the black state is switched to a white state havingtransmittance of about 15% or over, if the drive voltage ratioVp1/Vp2=1.25, it is comprehensive that the response time is lessenedwithout the overshoot. In this case, when Vp1/Vp2=0.8 or 1, the responsespeed is fast, but the overshoot is generated, contributing to a flickerof the display screen.

It is considered that this is because, when the drive voltage Vp1 isabout 5V or more, liquid crystal elements in a projection part of thedomain restriction structure start aligning. Namely, as shown in FIG.6A, the drive voltage Vp1 is divided into a voltage Vpt and a voltageVpn in a region of the projection 40, and the voltage Vpt smaller thanthe drive voltage Vp1 is applied to a liquid crystal molecule 45 on theregion of the projection 40. In this case, when the drive voltage Vp1 isabout 5V or less, as the voltage Vpt to the liquid crystal molecule onthe region of the projection 40 is a threshold or less of the alignmentof the liquid crystal molecule 45, the liquid crystal molecules 45 donot move. Accordingly, it is considered that when Vp1/Vp2=0.8 or 1, theoperation of the liquid crystal molecules excluding the region of theprojection 40 is dominant, therefore the response speed increases, theovershoot is generated.

On the other hand, when the drive voltage Vp1 is about 5V or more, asshown in FIG. 6B, as the voltage Vpt of the region of the projection 40is the threshold or more of the alignment of the liquid crystal molecule45, the liquid crystal molecule 45 starts moving. However, as thealignment direction of the liquid crystal molecule 45 is not immediatelystabilized, the entire response speed decreases. Accordingly, it isconsidered that when Vp1/Vp2=1.25, the operation of the liquid crystalmolecule 45 on the region of the projection 40 starts in the first frameperiod Tf1, and as the operation delays, the overshoot lowers.

In this method, when the black state is switched to the white statehaving transmittance of about 15% or more, if the drive voltage ratioVp1/Vp2=1.25, in comparison with Vp1/Vp2=1 and 0.8, the response speedcan be optimized without the overshoot.

As is apparent from the results of FIGS. 4 and 5, (1) when the displayof a certain pixel is switched from the black state to the lowbrightness halftone state, it is preferable that the drive voltage VP1of the first frame period Tf1 is set to be, for example, 1.25 times thedrive voltage VP2 of the second frame period Tf2 and on; (2) when theblack state is switched to the high brightness halftone state, it ispreferable that the drive voltage VP1 is equal to the drive voltage VP2;and (3) when the black state is switched to the white state, it ispreferable that the drive voltage VP1 is set to be, for example, 1.25times the drive voltage VP2. Accordingly, in the cases of (1) and (3)above, a waveform of FIG. 3C is preferable, and in the case of (2)above, the waveform of FIG. 3B is preferable. Incidentally, the above1.25 times are downright one example, and in case of (1) and (3) above,in principle, it is necessary to set as Vp1>Vp2.

FIG. 7 is a diagram showing the response characteristic of a preferabledrive voltage and its transmittance according to the embodiment of thepresent invention when the display of a certain pixel is switched asblack low brightness halftone →black→high brightnesshalftone→black→white→black. The black state at the drive voltage 0.5V isdisplayed for 4-frame periods from time t11, and the low brightnesshalftone at the target drive voltage Vp2=2.5V is displayed for 4-frameperiods from time t12. This case corresponds to the change from thefirst transmittance to the second transmittance, and as shown in FIG.3C, the drive voltage in the first frame period starting from time t12is set to Vp1=1.25×Vp2=3.1V, and the next second, third and forth frameperiods are set as the target drive voltage Vp2=2.5V, thereby switchingto the low brightness halftone of transmittance about 2% with superiorresponsiveness.

Next, the black state at the drive voltage 0.5V is displayed for 4-frameperiods from time t13, and the high brightness halftone at the targetdrive voltage Vp2=3.5V is displayed for 4-frame periods from time t14.This case corresponds to the change from the first transmittance to thethird transmittance, and as shown in FIG. 3B, the drive voltage in thefirst frame period starting from time t14 and in the next second, thirdand forth frame periods is set as Vp1=Vp2=3.5V, thereby switching to thehigh brightness halftone of transmittance about 12% without anovershoot.

Next, the black state at the drive voltage 0.5V is displayed for 4-frameperiods from time t15, and the white state at the target drive voltageVp2=5.5V is displayed for 4-frame periods from time t16. This casecorresponds to the change from the first transmittance to the fourthtransmittance, and as shown in FIG. 3C, the drive voltage in the firstframe period starting from time t16 is set as Vp1=1.25×Vp2=6.9V, and thenext second, third and fourth frame periods are set to the target drivevoltage Vp2=5.5V, thereby switching to the white state of transmittanceabout 16% without the overshoot.

In this method, in the liquid crystal display device according to thisembodiment, even in either case of switching from the black state to thelow brightness halftone state, from the black state to the highbrightness halftone state, and from the black state to the white state,the response time is shortened and also the switching is possiblewithout generating the overshoot.

FIG. 8 is a relational diagram between a drive voltage and acompensation voltage of the liquid crystal pixel according to theembodiment of the present invention. The target drive voltage Vp2 andtransmittance were taken in the axis of abscissas, and the drive voltageVp1 and the compensation voltage in the first frame period were taken inthe axis of ordinates. Here, the compensation voltage is a differencevoltage between the drive voltage Vp1 and the target drive voltage Vp2in the first frame period.

As described above, according to this embodiment, when the firsttransmittance for the black state is switched to the secondtransmittance for the low brightness halftone state, the drive voltageVp1 of the first frame period is set to be about 1.25 times the targetdrive voltage Vp2. Accordingly, the compensation voltage is set to beabout 0.25 times the target drive voltage Vp2.

Furthermore, when the first transmittance is switched to the thirdtransmittance for the high brightness halftone state, the drive voltageVp1 of the first frame period is substantially equal to the target drivevoltage Vp2. Accordingly, the compensation voltage is almost 0.

Furthermore, when the first transmittance is switched to the fourthtransmittance for the white state, the drive voltage Vp1 of the firstframe period is set to be about 1.25 times the target drive voltage Vp2.Accordingly, the compensation voltage is set to be about 0.25 times thetarget drive voltage Vp2.

Incidentally, in FIG. 8, specific numerical values of the first to thirdtarget drive voltages and values of the ratio of Vp1/Vp2 (1.25 times)can be different values according to a characteristic of the liquidcrystal, use of the liquid crystal display device, or the like.Furthermore, the compensation voltage correspondingly becomes valuesdepending on the characteristic of the liquid crystal, etc. Furthermore,each boundary of the first, second and third transmittances cannotalways be clearly defined. Accordingly, their characteristic diagramsbecome smooth curves as shown in FIG. 8.

In the liquid crystal display device according to the embodiment of thepresent invention, as described later, a relationship between the targetdrive voltage Vp2 and the compensation voltage is stored as a table, andas the drive voltage plus the compensation voltage is applied on theliquid crystal pixel, when the display of each liquid crystal pixel isswitched, the liquid crystal can be driven by the drive voltage havingoptimal characteristics of the response speed and the overshoot.

FIG. 9 is a schematic view of the entire of the liquid crystal displaydevice according to the embodiment of the present invention. The liquidcrystal display device according to the embodiment comprises a MVA typeliquid crystal panel 1; a drive control part 50 to which a video signalS10 is supplied; a gate driver part 51 to which a timing signal S11 issupplied from the drive control part 50, and which drives gate electrodelines of the MVA type liquid crystal panel 1; a compensation circuit 52for generating a compensation voltage signal S14 of the drive voltagefrom a target drive signal S12 in correspondence with the targettransmittance of the liquid crystal pixel; a drive voltage adjustmentcircuit 57 for generating a drive signal S13 of the liquid crystal pixelfrom the target dive signal S12 and the compensation voltage signal S14;and a source driver part 59 to which the drive signal S13 and the timingsignal S11 are supplied, and which drives the source electrode line ofthe MVA type liquid crystal panel 1.

Furthermore, the compensation circuit 52 comprises primary and secondaryframe memories 53, 54 for alternately storing the target drive signalS12 of each of the respective liquid crystal pixels of the MVA typeliquid crystal panel 1 in each frame period; and a display status changepixel detection circuit 55 for comparing data of the primary framememory 53 with data of the secondary frame memory 54, and detectingpixels of the changed display status, and outputting the compensationvoltage signal S14 to a drive voltage adjustment circuit 57. In thiscase, the display status change pixel detection circuit 55 refers to alookup table 56 storing relational data of the target drive voltage Vp2and the compensation voltage when the display status is changed from astatus of transmittance 0 shown in FIG. 8, and generates thecompensation voltage signal S14.

Namely, the target drive signal S12 in correspondence with thetransmittance of the pixels is output from the drive control part 50 insynchronism with the timing signal S11, and alternately stored in theprimary and secondary frame memories 53, 54 in each frame period. Inthis case, for example, when the first transmittance of a certain pixelis stored in the primary frame memory 53 in the first frame period andthe second transmittance of the pixel is stored in the secondary framememory 54 in the second frame period, the pixel is switched from thefirst transmittance to the second transmittance. This switching of thepixel display is detected by the display status change pixel detectioncircuit 55, which generates the compensation voltage signal S14 based ondata of the lookup table 56. This compensation voltage signal S14 isadded to the target drive signal S12 in the drive voltage adjustmentcircuit 57, and is supplied to a source driver part 59 as the drivesignal S13.

In this method, in the liquid crystal display device according to thisembodiment, as the liquid crystal pixel is driven based on data of thelookup table 56 acquired from the response characteristic of the liquidcrystal pixel, it is possible to optimize the characteristics of theresponse speed and the overshoot of the liquid crystal pixel.Furthermore, even when the liquid crystal pixel having the differentresponse characteristic is driven, it is possible to realize the optimalresponse characteristic at all times only by changing the data of thelookup table 56.

[Second Embodiment]

Next, a liquid crystal display device according to another embodiment ofthe present invention in which, in displaying a black, a predetermineddrive voltage is applied on liquid crystal molecules to be in advanceinclined, so that a response time is lessened when the black state isswitched to a halftone state, etc., will be explained.

As described above, as the liquid crystal molecules in the vicinity of aprojection of a MVA type liquid crystal panel are aligned vertically toan inclined plane of the projection, the liquid crystal molecules have aslight inclined angle even in a state that a drive voltage is notapplied. However, the inclination of the liquid crystal molecules in thevicinity of the projections only becomes a trigger which lets the otherliquid crystal molecules incline sequentially when the drive voltage isapplied, and the liquid crystal molecules away from the projections arealigned substantially vertically to a substrate in a state that thedrive voltage is not applied.

In the liquid crystal display device according to this embodiment of thepresent invention, when a black is displayed in the MVA type liquidcrystal panel, a predetermined drive voltage Voff is applied on theliquid crystal molecules to be in advance inclined, and the responsetime when the black state is switched to the halftone state, etc. islessened.

FIG. 10 is a cross-sectional view when a drive voltage is not applied onthe MVA type liquid crystal panel according to this embodiment. In theMVA type liquid crystal panel according to this embodiment, an electrode102 of an ITO transparent conductive inter-film, etc., a bank-likestructure 103 of a projection, etc., and a vertical alignment film 104are laminated on a lower face of a substrate 101 of glass, etc., and acommon electrode 108, the bank-like structure 103, and a verticalalignment film 107 are laminated on an upper face of a substrate 109 ofglass, etc., and liquid crystal molecules 105 are sealed uptherebetween, and further a polarization plate 106 is provided on theupper face of the substrate 101, and a polarization plate 110 isprovided on the lower face of a substrate 109.

When the MVA type liquid crystal panel according to this embodiment is,for example, operated in a normally black mode with a transmissionstructure, a transmission axis of the polarization plate 106 isstationed so as to be perpendicular to the transmission axis of thepolarization plate 110. In the MVA type liquid crystal panel, in a statethat the drive voltage is not applied between the electrode 102 and thecommon electrode 108, as the liquid crystal molecule 105 is alignedsubstantially vertically to the substrate 101, etc., the liquid crystalmolecule 105 does not have an optical characteristic of an opticalrotation, etc. Accordingly, lights 112 which became a linearpolarization by passing the polarization plate 106 cannot pass thepolarization plate 110, so that a black state of transmittance 0 can beobtained.

On the other hand, when the drive voltage is applied between theelectrode 102 and the common electrode 108, the inclination of theliquid crystal molecule 105 starts to have the optical characteristic,and the lights 112 slightly pass the polarization plate 110 to becomethe halftone state. When the drive voltage between the electrode 102 andthe common electrode 108 is further increased, the liquid crystalmolecule 105 is horizontalized to the substrate 101, etc, and apolarization plane of the lights 112 rotates at 90°, and thetransmittance of the polarization plate 110 is maximized. This case is awhite state.

FIG. 11 is an explanatory view in which in a state that the drivevoltage Voff is applied in the MVA type liquid crystal panel accordingto this embodiment of the present invention, a black is displayed. FIG.11A is its cross-sectional view and FIG. 11B is its plane view. As shownin FIG. 11A, in the MVA type liquid crystal panel according to thisembodiment, even when the black state is carried out, the drive voltageVoff is applied between the electrode 102 and the common electrode 108,and the liquid crystal molecule 105 is in advance inclined at only anangle θp from a direction vertical to the substrate 101, etc. Here, thedrive voltage Voff is set to be greater than a threshold voltage Vthstarting the inclination of the liquid crystal molecule 105, and alsosmaller than a value generating transmittance of the liquid crystalpanel.

Incidentally, as shown in the plane view of FIG. 11B, the inclinationdirection of the liquid crystal molecule 105 is a direction vertical tothe bank-like structure 103. Furthermore, since left and rightinclinations of the bank-like structure 103 are different from eachother, the liquid crystal molecules 105 are inclined leftward in aregion I and a region III of the liquid crystal panel, and rightward ina region II thereof.

In this method, according to this embodiment, the drive voltage Voffdisplaying a black is set to be higher than the threshold voltage Vth,so that the liquid crystal molecules 105 in the black state are inclinedat only the angle θp. Accordingly, when the black state is switched tothe halftone state, the liquid crystal molecules 105 can be inclined ina short time up to an angle corresponding to the halftone state, and theresponse time of the display can be lessened.

FIG. 12 is a diagram showing a relationship between the drive voltage Vpof the liquid crystal molecule 105 and the transmittance Tp of theliquid crystal panel. When the drive voltage Vp is incrementallyincreased from 0, as describe above, the inclination of the liquidcrystal molecule 105 starts at the threshold voltage Vth. However, evenif the drive voltage Vp exceeds the threshold voltage Vth, theinclination of the liquid crystal molecule 105 is still small, and thetransmittance Tp is substantially 0. The display is still a black.

When the drive voltage Vp exceeds 2V, the transmittance Tp incrementallyincreases, and the transmittance Tp becomes about 2% at the drivevoltage Vp about 2.5V, thereby reaching the low brightness halftonestate. Furthermore, when the drive voltage Vp is about 3.5V, thetransmittance Tp becomes about 10%, thereby reaching the high brightnesshalftone state, and when the drive voltage Vp is about 5V, thetransmittance Tp becomes about 15% or more, thereby reaching the whitestate.

In this method, as the MVA type liquid crystal panel according to thisembodiment has a region where the transmittance Tp is 0 even at thethreshold voltage Vth or more starting the inclination of the liquidcrystal molecule 105, the drive voltage Voff displaying a black can beset to be greater than the threshold voltage Vth, for example, 2V,whereby even in the black state, the liquid crystal molecule 105 can beinclined in advance at only the angle θp. Accordingly, when the blackstate is switched to the halftone state, etc., the liquid crystalmolecule 105 can be inclined in a short time up to an anglecorresponding to the halftone state, etc., and the response time of thedisplay can be shortened.

FIG. 13 is a diagram showing a relationship between the drive voltageVoff and a response time τ to a halftone when a state that the drivevoltage Voff is applied to display a black is switched to the halftonestate at the drive voltage Vp=2.5V. As shown in FIG. 13, the responsetime τ in case of the drive voltage Voff=0 is about 95 ms, but if thedrive voltage Voff=2V, the response time τ is reduced to about 65 ms.

In this method, the higher the drive voltage Voff displaying a black,the faster the response time when the black state is switched to thehalftone state. In this case, as shown in FIG. 12, since thetransmittance Tp of the liquid crystal panel is 0 until the drivevoltage Voff reaches about 2V, the drive voltage Voff is set to be about2V, thereby shortening only the response time without lowering displaycontrast of the liquid crystal panel.

Incidentally, the MVA type liquid crystal panel according to thisembodiment is shown as an example of using the bank-like structure 103for the purpose of determining the inclination direction of the liquidcrystal molecule 105 in FIG. 11. The present invention is applicable tothe whole of VA type liquid crystal panels such as a display panel whichuses a slit-like electrode in order to determine the inclinationdirection of the liquid crystal molecule 105, a display panel which usesa rubbed vertical alignment film, or the like.

FIG. 14 is a cross-sectional view of the MVA type liquid crystal panelaccording to the another embodiment of the present invention. In thisembodiment, the further greater drive voltage Voff is applied in a blackstate, and an inclination angle of the liquid crystal molecules isincreased, and the response time when the black state is switched to thehalftone state is further lessened.

This embodiment differs from the embodiment of FIG. 10 in that anoptical characteristic compensating linear phaser film 120 is providedbetween the transparent substrate 101 of glass, etc. and thepolarization plate 106. Since the linear phaser film 120 has an opticalcharacteristic reverse to that of the liquid crystal, the linear phaserfilm 120 can cancel the optical characteristic of the liquid crystal.

Namely, even if the greater drive voltage Voff is applied and theinclination angle θp of the liquid crystal molecule is increased, thelinear phaser film 120 can cancel the optical characteristic of theliquid crystal. Therefore, in the MVA type liquid crystal panellaminating the linear phaser film 120, the inclination angle θp of theliquid crystal molecule in the black state can be increased, and theresponse time from the black state to the halftone state can be morelessened.

In order to cancel the optical characteristic of the liquid crystal bylamination of the linear phaser film 120, the linear phaser film 120 inwhich an optical phase difference Δnd is about 10 nm is stationed sothat the delay phase axis 121 is vertical to a delay phase axis(inclination direction) of the liquid crystal molecule 105 as shown inFIG. 15, namely in parallel to the bank-like structure 103. This stationcauses the optical characteristic in the linear phaser film 120 reverseto that of the liquid crystal, and can cancel the optical characteristicof the liquid crystal.

FIG. 16 is a diagram showing a relationship between the drive voltage Vpand the transmittance Tp of the MVA type liquid crystal panel in whichthe linear phaser film 120 is laminated. The characteristic of the drivevoltage about 2V or more of FIG. 16 is equivalent to one in which thecharacteristic of the transmittance of FIG. 12 not laminating the linearphaser film is shifted in parallel downward by only the transmittancerelevant to the optical characteristic of the linear phaser film 120.Incidentally, in FIG. 16, the transmittance Tp is not 0 while the drivevoltage Vp is 0V to 2V, and this is because the inverse opticalcharacteristic is generated by lamination of the linear phaser film 120.

In the MVA type liquid crystal panel according to this embodiment, asshown in FIG. 16, since the drive voltage Vp for setting thetransmittance Tp to 0 is 2V or more, the high drive voltage Voff of 2Vor more can be applied in the black state. Accordingly, the inclinationangle of the liquid crystal molecule can be increased in correspondencewith the high drive voltage Voff of 2V or more, and the response timefrom the black state to the halftone state can be more diminished.Incidentally, when the optical phase difference Δnd of about 10 nm isprovided to a visual angle compensating phase difference film usuallyused in the MVA type liquid crystal panel, the same effect can berealized.

In case where the linear phaser films 120 are laminated, when thealignment directions of the liquid crystal molecules 105 differaccording to the region of the display panel, it is necessary that thedelay phase axis 121 of the linear phaser film 120 is perpendicular tothe delay phase axis (inclination direction) of the liquid crystalmolecule 105 in each region. In this case, it is preferable that thelinear phaser film 120 is formed inside the display panel, and isbrought as near as possible in proximity to the bank-like structure 13and the liquid crystal layer, and therefore a parallax of each region islessened.

FIG. 17 is a cross-sectional view of the MVA type liquid crystal panelin which the optical characteristic compensating linear phaser film 120is formed inside the display panel according to the another embodimentof the present invention. According to this embodiment, as the linearphaser film 120 is formed on the lower face of the substrate 101 ofglass, etc., and is near to the bank-like structure 103 and the liquidcrystal layer, the parallax of each region can be reduced.

FIG. 18 is a top view of the MVA type liquid crystal panel according tothe another embodiment of FIG. 17. According to this embodiment, as thebank-like structure 103 is formed zigzag, the alignment directions ofthe liquid crystal molecules 105 also become vertical to the bank-likestructure 103 in each of the regions IV, V and VI to be zigzag.Accordingly, the delay phase axis 121 of the linear phaser film 120 isstationed in a direction perpendicular to the delay phase axis(inclination direction) of the liquid crystal molecule 105 in each ofthe regions IV, V and VI, namely in parallel to the bank-like structure103.

In this method, according to this embodiment, as the delay phase axis121 of the linear phaser film 120 in each of the respective regions isstationed perpendicular to the delay phase axis (inclination direction)of the liquid crystal molecule 105, the optical characteristic of theliquid crystal can be cancelled by the linear phaser film 120, and itbecomes possible to apply the high drive voltage Voff in the blackstate. For this reason, the inclination angle θp of the liquid crystalmolecule in the black state is increased, and the response time from theblack state to the halftone state can be shortened.

[Third Embodiment]

Next, an explanation will be for a liquid crystal display device inwhich a response time is shortened when a black state is switched to ahalftone state, etc., and a liquid crystal display device which reducesan overshoot of a brightness to be generated when the display isswitched.

According to the first embodiment above, when the black state isswitched to the halftone state, etc., for example, the black state ofone frame just before switching to the halftone state is detected, and adrive voltage of a liquid crystal is adjusted by the detection results.However, since a response characteristic from the black state to thehalftone state, etc. is affected by not only the black state of the justpreceding one frame, but also the display of the frame further beforethe just preceding frame, a suitable drive cannot be made by detectingonly the black state of the just preceding frame, and there may be acase where an overshoot is generated in a brightness.

Then, in the liquid crystal display device according to this embodiment,when the black state is switched to the halftone state, etc., the blackstates of the just preceding frame and the further prior frame aredetected, and a suitable drive voltage is applied, so that the overshoot of the brightness is decreased.

FIG. 19 is a structural view of the liquid crystal display deviceaccording to the embodiment of the present invention. The liquid crystaldisplay device according to this embodiment comprises a compensationvoltage detection circuit 205 for detecting a drive voltage to becompensated from a video signal; a compensation just preceding voltagedetection circuit 202 for detecting the drive voltage one frame beforethe drive voltage to be compensated; and a just preceding displayvoltage frame memory 203 for storing the drive voltage detected by thecompensation just preceding voltage detection circuit 202, and the justpreceding display voltage frame memory 203 has a bit counter 204 forcounting the number of frames when each pixel has the same drive voltagein the continuous frame. Incidentally, a control signal for setting athreshold, etc. of a detection voltage is input from a control circuit201 to the just preceding display voltage frame memory 203. The framememory 203 and the bit counter 204 have regions and counters for thepixels, respectively.

Furthermore, the liquid crystal display device according to thisembodiment comprises a compensation voltage generation circuit 206 forgenerating a compensation voltage to be added to the drive voltage; acompensation judgement circuit 207 for judging whether or notcompensation is made from the drive voltage to be compensated and thejust preceding drive voltage; a multiplexer 208 for adding thecompensation voltage signal to the video signal; a panel drive circuit209 for driving a liquid crystal display panel 210 according to anoutput signal of the multiplexer 208; and the liquid crystal displaypanel 210.

In the liquid crystal display device according to this embodiment, forexample, when the response characteristic is compensated when switchingfrom the continuous black state to the halftone state, etc., the drivevoltage of the black state in the frame just before the compensatinghalftone state frame is detected by the compensation just precedingvoltage detection circuit 202, and the drive voltage is stored in thejust preceding display voltage frame memory 203.

When it is detected by the bit counter 204 that the black state justbefore the compensating halftone state frame continues in thepredetermined number of frames, and the compensating halftone drivevoltage is detected by the compensation voltage detection circuit 205,the compensation voltage is added to the drive voltage by themultiplexer 208.

An alignment state of the liquid crystal molecules displaying a black isnot necessarily in the initial state at all times, but differs dependingon the drive voltage of the preceding frame. However, if the black statecontinues, for example, in two frames, the alignment state of the liquidcrystal molecules becomes substantially an initial state irrespective ofthe drive voltage of the preceding frame. For this reason, since a statechange of the liquid crystal molecules is constant when the black stateis switched to the halftone state in this case, the optimal compensationvoltage can always be added to the drive voltage for displaying thehalftone. Accordingly, the response time is reduced for changing theblack state to the halftone state, and also the overshoot of thebrightness can be prevented.

FIG. 20 is an explanatory view showing a compensation principle of adrive method according to this embodiment. FIG. 20A is waveforms of thedrive voltage and transmittance in the case of non-compensation. Here,the axis of abscissas is a time, and scales are entered in each of a1-frame period T. Incidentally, the drive voltage is actually invertedin each of the 1-frame period and applied to liquid crystal molecules,but for conveniences of description of the response characteristic, itis denoted as absolute values.

When the compensation according to this embodiment is not made, as shownin FIG. 20A, even if a drive voltage Vp2 displaying a halftone in time 0is applied, transmittance does not rise immediately, and reaches targettransmittance Tp2 in time 2T and on.

FIG. 20B is a waveform when the drive voltage Vp1 greater than Vp2 isapplied in only the first frame period starting from time 0 in order toobtain the optimal drive voltage. In this case, the transmittance risesfrom time 0, and reaches transmittance Tp1 of a peak in time T, andthereafter falls to be 0 in time 2T. According to this embodiment, thedrive voltage Vp1 in which the transmittance Tp1 of a peak of FIG. 20Bis equal to a target transmittance Tp2 of FIG. 20A is used as the drivevoltage of the first frame. This is shown in FIG. 20C.

FIG. 20C is a waveform when the compensation of the responsecharacteristic was made by the drive method according to thisembodiment. According to this embodiment, the frames of the black statecontinue (−3T, −2T, −T), and also when the black state is switched tothe halftone state in time 0, the compensation of the drive voltage ismade. FIG. 20C is the case where the black state continues in a 2-frameperiod of a −2 frame (−2T) and a −1 frame (−T), and also the targetdrive voltage Vp2 corresponds to the halftone in time 0, and the drivevoltage Vp1 greater than the target drive voltage Vp2 is applied in thefirst frame period (0 to T). According to the drive method of thisembodiment, it is possible to reach the target transmittance Tp1=Tp2 ina 1-frame period without generating the overshoot.

Next, when the drive voltage of the first frame (0 to T) is establishedby the above drive method of the first embodiment, the description willbe made that the overshoot is generated in the transmittance Tp1 of thefirst frame (0 to T) due to influences of the −2 frame (−2T to −T).

As shown in FIG. 21, when the −2 frame (−2T to −T) is the halftone stateand the drive voltage is Vp2, even if the drive voltage of the −1 frame(−T to 0) is 0, as the compensation voltage Vp1 is applied, theovershoot may generate in the transmittance Tp1 of the first frame (0 toT). This is because the inclination angle of the liquid crystalmolecules inclined in the −2 frame (−2T to −T) is not returned fully toan initial state in the 1-frame (−T to 0). As is understood from FIG.21, in addition to the just preceding frame, in correspondence with thedrive voltage of the −2 frame period before that, it is preferable to bejudged whether or not the compensation voltage is applied.

FIG. 22 is a diagram showing a relationship between a drive voltage Vn−2of the −2 frame (−2T to −T) and maximum transmittance Tp1 of the firstframe (0 to T) when the drive voltage Vn−1 of the −1 frame (−T to 0) is,for example, 1V. As shown in FIG. 22, when the drive voltage Vn−2 of the−2 frame (−2T to −T) changes, the maximum transmittance Tp1 of the firstframe (0 to T) changes largely. Accordingly, according to thisembodiment, not only the drive voltage Vn−1 of the just prior −1 frame(−T to 0), but also the drive voltage Vn−2 of the further prior −2 frame(−2T to −T) are detected, and the drive voltage Vp1 of the first frame(0 to T) is determined. Namely, when the black state, etc. continues inthe just preceding 2-frame period, the drive voltage Vp1 of the firstframe (0 to T) is established.

FIG. 23 is a diagram showing a relationship between the drive voltageVn−3 of a −3 frame and the maximum transmittance Tp1 of the first frame(0 to T) under the same conditions of FIG. 22. As shown in FIG. 23, thedrive voltage Vn−3 of the −3 frame (−3T to −2T) is smaller in influencesexerted on the maximum transmittance Tp1 of the first frame (0 to T)than the case of the drive voltage Vn−2 of the −2 frame (−2T to −T)shown in FIG. 22. Accordingly, according to this embodiment, only whenthe same drive voltage continues in the 2-frame period, the drivevoltage of the first frame (0 to T) is set to be Vp1, whereby the changeof transmittance of the first frame (0 to T) is optimized.

In this method, in the liquid crystal display device according to thisembodiment, when the black state continues in the 2-frame periods andalso the black state is switched to the halftone state after that, thedrive voltage Vp1 greater than the target drive voltage Vp2 is appliedon the first frame period (0 to T) displaying the halftone. For thisreason, in the state change when the liquid crystal molecules areswitched from the black state to the halftone state, the change is madefrom almost an initial state and the overshoot of the brightness can beprevented.

Incidentally, in the MVA type liquid crystal panel, since when the drivevoltage is applied, the inclination alignment of the liquid crystalmolecules is spread from a bank-like structure, only part of pixelsresponds in the 1-frame period, and a bound may generate in the secondframe (T to 2T) as shown by a dotted line in FIG. 20C. In the case, thedrive voltage Vp1 is continuously applied in the first and second frames(0 to T, T to 2T), thereby reducing the bound.

Next, the description will be made that when temperature of the liquidcrystal panel increases, the overshoot is generated in the transmittanceof the liquid crystal panel. FIG. 24 is a waveform diagram of the drivevoltage and the transmittance when temperatures of the liquid crystalpanel rise. As shown in FIG. 24, according to the drive method of thisembodiment, even when the drive voltage Vp1 is applied in the firstframe period (0 to T), as the response of the liquid crystal isaccelerated by an increase in the temperatures, the overshoot may begenerated in the transmittance of the first frame (0 to T).

FIG. 25 shows a change of the maximum transmittance Tp1 of the firstframe (0 to T) when temperatures of the display panel are 25° C., thedrive voltage Vp1 of the first frame is 4.0V, 3.5v and 3.0V, and alsowhen the drive voltage Vn−1 of the −1 frame (−T to 0) changes. As shownin FIG. 25, when the drive voltage Vp1 of the first frame (0 to T) is3.0V, if the drive voltage Vn−1 of the −1 frame (−T to 0) changes from0V to 2V, the maximum transmittance Tp1 of the first frame (0 to T)changes from about 0% to 2%.

FIG. 26 shows the maximum transmittance Tp1 of the first frame (0 to T)when temperatures of the display panel are 45° C. under the sameconditions as FIG. 25. As shown in FIG. 26, when the drive voltage Vp1of the first frame (0 to T) is 3.0V, if the drive voltage Vn−1 of the −1frame (−T to 0) changes from 0V to 2V, the maximum transmittance Tp1 ofthe first frame (0 to T) changes from about 3% to 7%. In this method,when the temperatures of the liquid crystal panel increase, thetransmittance of the liquid crystal panel increases, and when thecompensation voltage Vp1 is applied as shown in FIG. 24, the overshootis generated in the transmittance, and the accurate brightness cannot bedisplayed.

Then, in the liquid crystal display device according to this embodiment,in the compensation voltage generation circuit 206 shown in FIG. 19,when the temperatures rise, a temperature compensation is made so as tolower the drive voltage Vp1 of the first frame (0 to T), and thisprevents the generation of the overshoot in the transmittance of thedisplay panel. Namely, in FIG. 20C, when the temperatures of the panelrise, the drive voltage Vp1 of the first frame (0 to T) is set to belower as shown by a broken line.

Furthermore, as shown in FIGS. 25 and 26, when the drive voltage Vn−1 ofthe −1 frame (−T to 0) changes, the maximum transmittance Tp1 of thefirst frame (0 to T) also changes, and as shown in FIG. 12, if the drivevoltage is 2V or less, the transmittance of the display panel issubstantially 0. Accordingly, according this embodiment, when the blackstate is carried out in pixels, the maximum drive voltage is applied ona pixel electrode in the range of displaying a black. Namely, all thedrive voltages Vn−1 of 2V or less is summarized to 2V, whereby thecalculation of the drive voltage Vp1 of the first frame (0 to T) by thedrive voltage Vn−1 of the just preceding display frame (−T to 0) issimplified, thereby decreasing a process load of a drive circuit.Furthermore, when the drive voltage Vn−1 of the −1 frame (−T to 0) ishigh, as the liquid crystal molecules have been aligned aslant inadvance, the bound can be decreased.

The above embodiment explained the MVA type liquid crystal panel havingthe plurality of regions where the liquid crystals are verticallyaligned, but the present invention is not limited to the MVA type liquidcrystal panel, but is applicable to even the general VA type liquidcrystal panel.

INDUSTRIAL APPLICABILITY

As explained hereinabove, according to the present invention, it ispossible to provide the liquid crystal display device in which, when theMVA or VA type liquid crystal panel in which n type liquid crystals arevertically aligned is driven, the response time when the black state isswitched to the low brightness halftone state is shortened, and theovershoot when the black state is switched to the high brightnesshalftone state or the white state is decreased; and its drive method.

1. A liquid crystal display device, comprising: a liquid crystalprovided between a pixel electrode and a counter electrode to which adrive voltage is applied; a domain restriction structure for restrictingan alignment of the liquid crystal so that the alignment of the liquidcrystal is substantially vertical when non-voltage is applied,substantially parallel when a predetermined voltage is applied, andinclined when a smaller voltage than the predetermined voltage isapplied, and further a direction that the alignment of the liquidcrystal is inclined is set to be a plurality of parts in each pixel whena voltage smaller than the predetermined voltage is applied; and a drivecircuit in which when the pixel is changed from a first transmittance toa second transmittance greater than the first transmittance, a voltagegreater than a first target drive voltage corresponding to the secondtransmittance is applied between the pixel electrode and the counterelectrode in a first period of changing to the second transmittance, andthe first target display voltage is applied between the pixel electrodeand the counter electrode in a second period after the first period. 2.The liquid crystal display device according to claim 1, wherein when thepixel is changed from the first transmittance to a third transmittancegreater than the second transmittance, the drive circuit applies asecond target drive voltage corresponding to the third transmittancebetween the pixel electrode and the counter electrode in the firstperiod of changing to the third transmittance.
 3. The liquid crystaldisplay device according to claim 2, wherein when the pixel is changedfrom the first transmittance to a fourth transmittance greater than thethird transmittance, the drive circuit applies a voltage greater thanthe third target drive voltage corresponding to the fourth transmittancebetween the pixel electrode and the counter electrode in the firstperiod of changing to the fourth transmittance, and applies the thirdtarget drive voltage between the pixel electrode and the counterelectrode in a second period after the first period.
 4. A method fordriving a liquid crystal display device including a liquid crystalprovided between a pixel electrode and a counter electrode to which avoltage is applied, and a domain restriction structure for restrictingan alignment of the liquid crystal so that the alignment of the liquidcrystal is substantially vertical when non-voltage is applied,substantially parallel when a predetermined voltage is applied, andinclined when a smaller voltage than the predetermined voltage isapplied, and further a direction that the alignment of the liquidcrystal is inclined is set to be a plurality of parts in each pixel whena voltage smaller than the predetermined voltage is applied, the methodcomprising: when the pixel is changed from a first transmittance to asecond transmittance greater than the first transmittance, applying avoltage greater than a first target drive voltage corresponding to thesecond transmittance between the pixel electrode and the counterelectrode in a first period of changing to the second transmittance; andapplying the first target display voltage between the pixel electrodeand the counter electrode in a second period after the first period.